Town
I'm not sure what you envision for the town/city Mike lives in.  I see it as a small, touristy place in the mountains of Colorado.  What do you think of the name Celes Peak... named for the fact that the natural rifts to Celestria are nearby?  Though no Terrestian would know that was the reason for the name and it's changed through the years dropping the ...tria.  Now this isn't set in stone if you want something different... none of it is set in stone yet.

Changes
I thought, instead of being a guard in Celestria (his world), Sevrin could be a monitor in Terrestia (her world).  He'd already have the house that way.  Also he is posing as a reclusive author of mysteries.  Jerek is the name of the badguy.

some brainstorming

Badguy should decide to come after Mike... first because he wants to destroy the way for more portals from Sevrin's home, and second because he likes killing pretty young women.  He doesn't just kill them though, he terrorizes them first.

 

Sevrin part one intro

 He is called to a meeting to find out badguy is gone. 

  They don't know how he escaped.  

Soon they get word from Mike's world that there have been "copycat" murders.   Murders that are just like some unsolved murders from 10 years ago.  

 Sevrin is sent to the real world to find badguy and return him to prison and also to get rid of any accomplices and evidence.